A concrete pump is one of widely used concrete machinery presently. The concrete pump generally includes a hopper, a delivery cylinder, a distributing valve and a delivery pipe. The hopper is adapted to store concrete slurry. The delivery cylinder makes reciprocating movements under driving of a hydraulic cylinder. The distributing valve is used to communicate the delivery cylinder with the hopper during the first predetermined time period so that the delivery cylinder sucks material, specifically appropriate amount of concrete slurry; and to communicate the delivery cylinder with the delivery pipe during the second predetermined time period so that the delivery cylinder pumps material, specifically pushes the sucked concrete slurry into the delivery pipe and conveys the sucked concrete slurry to a predetermined position under pressure of the delivery cylinder. The distributing valve is one of the key components for the concrete pump.
Distributing valves for the concrete pump mainly comprise a gate-type distributing valve, an S-type distributing valve, a C-type distributing valve and a skirt valve.
The gate-type distributing valve makes the delivery cylinder suck and pump material mainly by means of the up-down movement of two gates in the distributing valve, which communicates a delivery cylinder with an outlet of a hopper during the first predetermined time period to make the delivery cylinder suck material and communicates the delivery cylinder with a delivery pipe during the second predetermined time period via a Y-type pipe to make the delivery cylinder pump material. The advantage of the gate-type distributing valve is that the concrete pump has a better sucking performance and better pumping efficiency. In particular for coarse aggregate concrete, the above-mentioned advantage is more significant. However, the disadvantage of the gate-type distributing valve is that the pressure of the concrete slurry in the delivery pipe is limited by the fitting position of the periphery of the gate since the position between the delivery cylinder and the delivery pipe is realized by switching the gates positions. Thus the gate-type distributing valve can not meet the requirement of pumping concrete slurry at a high pressure.
Referring to FIG. 1, a structural view of an S-type distributing valve in the prior art is shown. In FIG. 1, a hopper 110 is shown in double dot dash line. The S-type distributing valve includes an S-type bend pipe 120, which is mounted in the hopper 110. The input end of the S-type bend pipe 120 may swing laterally in the hopper 110 under the driving of a driving mechanism 130 to communicate with the two delivery cylinders 140 alternately. An output end of the S-type bend pipe 120 is in communication with a delivery pipe located outside of the hopper 110. Thus, the two delivery cylinders 140 may pump concrete slurry to the delivery pipe via the S-type bend pipe 120 alternately. The advantage of the S-type distributing valve is that, since the high pressure produced during pumping material by the delivery cylinder mainly acts on the inner wall of the S-type bend pipe, there is a uniform tensile stress on the whole S-type bend pipe which has a circular cross section, therefore the S-type distributing valve may withstand relatively great pressure. The operating pressure may be up to 16 Mpa or even more. Therefore, by utilizing the S-type distributing valve, the concrete pump may pump concrete slurry to a longer distance or to a higher position, so as to meet the requirement of pumping the concrete slurry at high pressure. However, the disadvantage of the S-type distributing valve is that the S-type bend pipe of the S-type distributing valve is located in the hopper 110 and occupies a part of volume of the hopper 110, so as badly affects the flowing of concrete slurry, thus affecting the sucking performance of the concrete pump. In addition, the S-type bend pipe is located in the hopper 110, so that it leads to material deposit in the hopper easily.
The C-type distributing valve and the skirt valve have the similar working principle as the S-type distributing valve, and thus have the same defects.
In view of the defects of the above existing distributing valves, Chinese patent publication No. CN 101245866A discloses a distributing valve for a concrete pump. The distributing valve includes a valve body and a valve core which is arranged in the valve body. The valve body is provided with a material outlet, a first material suction port and a second material suction port. The valve core is provided with an upper extension shaft and a lower extension shaft, through which the valve core is rotatably mounted on the valve body, a bearing and a sealing mechanism are respectively mounted between the upper extension shaft and the valve body and between the lower extension shaft and the valve body; the valve core takes the axis of the upper extension shaft and the lower extension shaft as a central line, and rotates respect i n g to the valve body for a certain angle to form a left limit position and a right limit position; the valve core also comprises a side opening and a material inlet which is communicated with a hopper. When the valve core rotates to the left limit position, the side opening is communicated with the first material suction port. When the valve core rotates to the right limit position, the side opening is communicated with the second material suction port.
When the concrete distribution valve disclosed in CN 101245866A is used, the usage volume of the hopper may be increased due to the separate arrangement of the distribution valve and the hopper, so that the blades in the hopper stir more sufficiently; the material inlet is oriented straight downward, so as to facilitate material input, in particular for pumping of coarse aggregate, and to improve the material suction performance of the concrete pump, to avoid the material depositing in the hopper and to make the cleaning of the hopper very easily; during the pumping process, as a passage which is communicated with the first material suction port, the second material suction port and the material outlet is arranged between the valve core and the valve body of the distribution valve, the valve body is able to keep the passage sealed, thus the requirement of pumping concrete slurry at a high pressure can be met. But the distribution valve has the following defects:
In order to meet the requirement of pumping concrete slurry at a high pressure, a very high pressure shall be established in the valve body; as the valve body and the valve core are rotatably matched at the matching point, so it is essential to keep the performance of the dynamic seal at the matching point of the valve body and the valve core so as to ensure the working performance of the distribution valve. In order to ensure the sealing of the rotation match between the valve body and the valve core, in CN 101245866A, the upper end of the valve core is provided with an upper extension shaft and a step surface, and the lower end is provided with a lower extension shaft and a step surface so as to arrange a sealing gasket between the bottom surface of the cover plate and the valve core as well as between the valve body and the bottom surface of the valve core; in order to increase the service life of the distribution valve, it is also needed to arrange an abrasion resistance plate between the cover plate and the sealing gasket as well as between the valve body and the sealing gasket; in order to facilitate switching the state of the distribution valve, a guide plate is also arranged between the abrasion resistance plate and the sealing gasket. The above said configuration makes the distribution valve have very complex structure, therefore it leads to complex and difficult production process, and it is difficult to ensure the operation reliability of the distribution valve. Furthermore, the valve core can move up and down, the fit clearance of any step surface of the distribution valve can be embodied in the fit clearance of another step surface, so that the upper and lower two step surfaces will enlarge the fit clearance between the valve body and the valve core, decrease the sealing useful-life between the valve body and the valve core and thereby decrease the serve life of the distribution valve.
As the upper extension shaft and the lower extension shaft are rotatably connected to the valve body respectively, the complex structure and the sealing requirement make the rotation fit surface relatively large between the valve body and the valve core, so that the power required by the state switching of the distribution valve is increased, and thereby the power consumption of the concrete pump vehicle is increased.